“Add Themes” on WordPress Admin not loading

I’m trying to browse new WordPress Themes but the “Add Themes” page on my WordPress Admin is not loading. It keeps showing the following message:

“An unexpected error occurred. Something may be wrong with www.remarpro.com or this server’s configuration. If you continue to have problems, please try the support forums.”

My cookies are enabled and I have no idea what the issue could be. Thanks for any advice you can share.

The page I need help with: [log in to see the link]